Conventionally, a portable electronic device such as a mobile phone or a tablet PC sometimes needs to transmit audio data (ex. music file) to an external electronic device such as a speaker or an earphone. By this way, the user can listen to the audio data with a better quality or with a louder volume, or listen to the audio data without disturbing other people.
FIG. 1 is a schematic diagram illustrating how a portable electronic device transmits audio data to an external electronic device. As illustrated in FIG. 1, the portable electronic device 101 comprises a decoder 105 and a transmitting interface 107. The decoder 105 receives audio data AD_a from the audio source AS. In this example, the audio data AD_a follows an audio format MP3 (MPEG-1 Audio Layer-3) or AAC (Advanced Audio Coding). The decoder 105 decodes the audio data AD_a to generate the audio data AD_b, which follows an audio format PCM (Pulse-code modulation), such that the audio data AD_b can be mixed with other audio data.
After that, the transmitting interface 107 encodes the audio data AD_b again to generate the audio data AD_c, which follows the audio standard AAC, SBC (sub-band coding), or aptX. By this way, the receiving interface 109 in the external electronic device 103 can receive the audio data AD_c. Also, the audio data AD_c is decoded by the decoder 111 in the external electronic device 103, thereby the audio data AD_d following the audio format PCM is generated. Finally, the external electronic device 103 plays the audio data AD_d.
However, the above-mentioned mechanism needs several encoding/decoding operations. For more detail, a decoding operation is needed between the audio data AD_a and AD_b, an encoding operation is needed between the audio data AD_b and AD_c, and another decoding operation is needed between the audio data AD_c and AD_d. Therefore, the quality of the audio data may decrease due to these encoding/decoding operations.